Domestic pet turns on it without a sound (5)
I believe the answer is:
tacit
'without a sound' is the definition.
(tacit can mean implied or unspoken)
'domestic pet turns on it' is the wordplay.
'domestic pet' becomes 'cat'.
'turns' says the letters should be written in reverse.
'on' means one lot of letters go next to another.
'cat' backwards is 'tac'.
'tac'+'it'='TACIT'
(Other definitions for tacit that I've seen before include "Implied, unstated" , "Unvoiced" , "Implied, not spoken" , "Unspoken but understood" , "Aircraft engine casing" .)